Supporting an assisted satellite based positioning

ABSTRACT

For supporting a satellite based positioning of a mobile arrangement ( 30,40 ) with assistance data, a communication network converts parameters of a dedicated orbit model describing a movement of a satellite ( 50,60 ), which dedicated orbit model is defined for a particular satellite based positioning system, into parameters of a common orbit model describing a movement of a satellite ( 50,60 ). Alternatively or in addition, the network replaces a reference value that is based on a satellite based positioning system time in available parameters of an orbit model by a reference value that is based on a communication system time. After the parameter conversion and/or the reference value replacement, the parameters are provided as a part of assistance data for the satellite based positioning. Alternatively or in addition, a set of data is transmitted in one direction between the mobile arrangement and the communication network, which is independent of the employed positioning mode.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of International Application SerialNo. PCT/IB2005/001638 filed Jun. 13, 2005.

TECHNICAL FIELD

Methods are shown for supporting a satellite based positioning of amobile arrangement with assistance data and using assistance data. Theinvention relates equally to an apparatus supporting a satellite basedpositioning of a mobile device with assistance data and to apparatussupporting a satellite based positioning of the mobile arrangement usingassistance data. The invention relates equally to corresponding softwarecodes and to corresponding software program products.

BACKGROUND

Currently there are two operating satellite based positioning systems,the American system GPS (Global Positioning System) and the Russiansystem GLONASS (Global Orbiting Navigation Satellite System). In thefuture, there will be moreover a European system called GALILEO. Ageneral term for these systems is GNSS (Global Navigation SatelliteSystem).

For GPS, for example, more than 20 satellites—also referred to as spacevehicles (SV)—orbit the earth. Each of the satellites transmits twocarrier signals L1 and L2. One of these carrier signals L1 is employedfor carrying a navigation message and code signals of a standardpositioning service (SPS). The L1 carrier phase is modulated by eachsatellite with a different C/A (Coarse Acquisition) code. Thus,different channels are obtained for the transmission by the differentsatellites. The C/A code is a pseudo random noise (PRN) code, which isspreading the spectrum over a nominal bandwidth of 20.46 MHz. It isrepeated every 1023 bits, the epoch of the code being 1 ms. The bits ofthe C/A code are also referred to as chips. The carrier frequency of theL1 signal is further modulated with the navigation information at a bitrate of 50 bit/s. The navigation information comprises in particular atimestamp indicating the time of transmission and ephemeris and almanacparameters.

GPS ephemeris and almanac parameters are basically satellite orbitparameters for a short-term polynomial orbit model of the true satellitetrajectory. The parameters are maintained and updated at a GPS controlserver and further updated at the satellites. Based on availableephemeris or almanac parameters, an algorithm can estimate the positionof the satellite for any time while the satellite is in the respectivedescribed section. The polynomial orbit models have only one degree offreedom, that is, time. The time base for ephemeris and almanacparameters is the GPS time, namely the GPS time-of-week (TOW). Thesatellite position calculation is basically an extrapolation of thesatellite positions along the orbit as a function of time starting froma known initial position. The initial position is also defined byparameters in the ephemeris and almanac data. A time-stamp moreoverindicates when the satellite is at the given initial orbital position.The time-stamps are called time-of-ephemeris (TOE) for ephemerisparameters and time-of-applicability (TOA) for the almanac parameters.Both the TOE and TOA are referenced into GPS TOW.

Ephemeris parameters can generally be used only during 2-4 hours fordetermining the position of a satellite, due to the rather short-termfitting. On the other hand, a better accuracy can be achieved with thisshort fit than with a longer fit. The achievable accuracy is 2-5 meters.Almanac parameters, in contrast, can be used for a coarse satellitepositioning even for weeks, but they are not suitable for the actualaccurate positioning due to the poor accuracy resulting from thelong-term fit and also from a smaller number of parameters. Ephemerisand almanac data are broadcast from the GPS satellites in a formatspecified in the open GPS interface control document (ICD) calledICD-GPS-200. Currently, all GPS receivers have to support this format.

A GPS receiver of which the position is to be determined receives thesignals transmitted by the currently available satellites, and itdetects and tracks the channels used by different satellites based onthe different comprised C/A codes. For the acquisition and tracking of asatellite signal, a signal received by a radio frequency (RF) portion ofthe GPS receiver is first converted into the baseband. In a basebandportion, frequency errors, for instance due to the Doppler effect, areremoved by a mixer. Then, the signal is correlated with replica codesthat are available for all satellites. The correlation can be performedfor example using a matched filter. The correlation values can furtherbe integrated coherently and/or incoherently in order to increase thesensitivity of the acquisition. A correlation value exceeding athreshold value indicates the C/A code and the code phase, which arerequired for despreading the signal and thus to regain the navigationinformation.

Then, the receiver determines the time of transmission of the codetransmitted by each satellite, usually based on data in the decodednavigation messages and on counts of epochs and chips of the C/A codes.The time of transmission and the measured time of arrival of a signal atthe receiver allow determining the time of flight required by the signalto propagate from the satellite to the receiver. By multiplying thistime of flight with the speed of light, it is converted to the distance,or range, between the receiver and the respective satellite. Further,the receiver estimates the positions of the satellites at the time oftransmission, usually based on the ephemeris parameters in the decodednavigation messages.

The computed distances and the estimated positions of the satellitesthen permit a calculation of the current position of the receiver, sincethe receiver is located at an intersection of the ranges from a set ofsatellites.

Similarly, it is the general idea of GNSS positioning to receivesatellite signals at a receiver which is to be positioned, to measurethe time it took the signals to propagate from an estimated satelliteposition to the receiver, to calculate from this propagation time thedistance between the receiver and the respective satellite and furtherthe current position of the receiver, making use in addition of theestimated positions of the satellites. The European Satellite NavigationSystem, Galileo, can be expected to have an ICD of its own. According tothe draft “L1 band part of Galileo Signal in Space ICD (SIS ICD)”, 2005,by Galileo Joint Undertaking, the Galileo ICD will be quite close to theGPS ICD, but not exactly the same. There will be Galileo ephemeris andalmanac data, and both will be related to a Galileo system time.

A GPS positioning can be performed in three different positioning modes.The first mode is a standalone GPS based positioning. This means thatthe GPS receiver receives signals from GPS satellites and calculatesfrom these signals its position without any additional information fromother sources. The second mode is a network-assisted mobile stationbased GPS positioning. For this mode, the GPS receiver may be associatedto a mobile communication device. The GPS receiver can be integratedinto the mobile communication device or be an accessory for the mobilecommunication device. A mobile communication network provides assistancedata, which is received by the mobile communication device and forwardedto the GPS receiver to improve its performance. Such assistance data canbe for example at least ephemeris, position and time information. Thepositioning calculations are performed also in this case in the GPSreceiver. The third mode is a network-based mobile station assisted GPSpositioning. For this mode, the GPS receiver is associated as well to amobile communication device. In this mode, a mobile communicationnetwork provides at least acquisition assistance and time informationvia the mobile communication device to the GPS receiver for supportingthe measurements. The measurement results are then provided via themobile communication device to the mobile communication network, whichcalculates the position. The second and the third approach are alsoreferred to in common as assisted-GPS (A-GPS). If the assistance datacomprises a reference position and ephemeris data for a particularsatellite, for example, the GPS receiver may determine the approximatesatellite position and motion and thus limit the possible propagationtime of the satellite signal and the occurring Doppler frequency. Withknown limits of the propagation time and the Doppler frequency, also thepossible code phases that have to be checked can be limited.

Assistance data for A-GPS has been specified and standardized for allcellular communication systems. The delivery of assistance data is buildon top of cellular communication system specific protocols, namely RRLPfor the Global System for Mobile Communications (GSM), IS-801 for CodeDivision Multiple Access (CDMA), RRC for Wideband CDMA (WCDMA) and OMASUPL. The mobile station assisted mode is currently deployed in CDMAnetworks in the U.S.A. for positioning of emergency calls.

There are many common features in all of the cellular protocols, forexample, the supported GPS modes. That is, all cellular protocolssupport mobile station based GPS, mobile station assisted GPS andstandalone GPS. Further, all protocols have a high dependency on GPS. Asindicated above, the assistance data that is provided for A-GPS by acellular communication network may comprise satellite navigation dataincluding GPS ephemeris and almanac data. All cellular protocols for GPSassistance data define to this end ephemeris and almanac datainformation elements (IE) with only slight differences. The ephemerisand almanac IEs defined in the cellular protocols are practicallyidentical with those defined in the ICD-GPS-200. Thus, they have alsothe same limitations and expected accuracy as the ephemeris and almanacdata which is broadcast by the satellites. This correspondence makes iteasy for a GPS receiver to use the assistance data in positioncalculations, as it requires practically no conversions or extrasoftware. Also a GPS ionosphere model is sent over the cellular linkaccording to all cellular protocols. The GPS assistance data elementsare linked to GPS time according to all cellular protocols. Moreover,the acquisition assistance is tailor-made for GPS only and cannot beused for position calculation in the mobile station according to allcellular protocols. Finally, all data elements are indexed in accordancewith the GPS satellite constellation according to all cellularprotocols.

However, while there are many common features in all of the GPS relatedcellular protocols, there are also differences. This means that terminalsoftware receiving the assistance data has to either have an adaptationlayer for the cellular protocols or support only some of the cellularprotocols. Moreover, the differences in the cellular protocols,especially in the message contents, have effects on the A-GPSperformance in terms of time-to-first fix and sensitivity.

A further problem is that in order to use the ephemeris or almanacparameters for predicting accurately the expected satellite code phasesand Doppler frequencies in the GPS receiver for the initial signalacquisition, the assistance data from the network has to also include anaccurate GPS TOW assistance. In GSM and WCDMA networks, an accurate GPSTOW delivery requires deployment of Location Measuring Units (LMU) atevery cellular base station, which are able themselves to acquire andevaluate GPS signals. LMUs, however, are expensive and require acontinuous maintenance.

Moreover, the current ephemeris and almanac data formats in the cellularprotocols are based on formats defined specifically for GPS. Assistancedata will also be of importance for Galileo, in order to ensure that theperformance of Galileo will be equal to A-GPS. It can be expected thatthe Galileo ephemeris format will be different from the GPS ephemerisand almanac formats so that the GPS assistance data format can notsimply be used for Galileo as well. If Galileo ephemeris is differentfrom GPS ephemeris, the cellular standards have to be augmented withGalileo specific information elements, and the use of Galileo for apositioning requires extra software in the receivers. Moreover, Galileoand GPS may have a different quality of service, that is, the Galileoephemeris data may be more accurate than the GPS ephemeris data,resulting in a better accuracy of a Galileo-based positioning. Moreover,Galileo and GPS ephemeris parameters may have different life spans. Inthis case, simultaneous assistance data updating is not possible butassistance data updates need to be scheduled independently for Galileoand GPS.

Thus, there are various problems with the current GPS assistance data.

It has been proposed to augment 3GPP GPS assistance data elements forGalileo signals by modifying the indexing of the ephemeris data elementsso that the indexing could also include Galileo satellites. The formatof the ephemeris data would then be essentially the same for GPS andGalileo satellites. With this solution, GPS and Galileo assistance datawould still be restricted to the limitations of the current GPSephemeris and almanac data, and also a GPS TOW delivery is stillrequired.

Further, it is known to enhance the accuracy and integrity of orbitmodels by means of correction data. The European GeostationaryNavigation Overlay Service (EGNOS) and the Wide Area Augmentation System(WAAS), for instance, determine GPS correction data, which take account,for example, of GPS signal delays caused by the atmosphere and theionosphere. The correction data is transmitted via geostationarysatellites and the data can be received by suitable GPS receivers and beused for increasing the accuracy of a GPS based positioning. Further,differential GPS (DGPS) corrections had been introduced for mitigatingthe effect of selective availability. They are suited to removeatmosphere effects and satellite position and clock drifts. WAAS, EGNOSand DGPS corrections are always bound to a single set of ephemeredes,though. When long-term satellite orbital parameters are used instead ofnormal ephemeris parameters, WAAS, EGNOS and DGPS corrections cannot beused, because they are bound to the normal ephemeris data.

SUMMARY OF THE INVENTION

Alternatives are provided to the conventional provision and use ofassistance data for a satellite based positioning of a mobilearrangement.

I

According to a first aspect of the disclosure, a first method isproposed for supporting a satellite based positioning of a mobilearrangement with assistance data, wherein the mobile arrangement isadapted to communicate with a communication network and to acquiresignals transmitted by satellites of at least one satellite basedpositioning system. The method comprises converting in the communicationnetwork available parameters of a dedicated orbit model describing amovement of a satellite, which dedicated orbit model is defined for aparticular satellite based positioning system, into parameters of acommon orbit model describing a movement of a satellite. The methodfurther comprises providing the converted parameters as a part ofassistance data for the satellite based positioning.

According to the first aspect of the disclosure, moreover a secondmethod is proposed for supporting a satellite based positioning of amobile arrangement using assistance data, wherein the mobile arrangementis adapted to communicate with a communication network and to acquiresignals transmitted by satellites of at least one satellite basedpositioning system. This method comprises receiving at the mobilearrangement assistance data from the communication network includingparameters of a common orbit model describing a movement of a satellite.The method further comprises estimating a position of a satellite of theat least one satellite based positioning system based on the receivedparameters of the common orbit model.

According to the first aspect of the disclosure, moreover a networkelement for a communication network supporting a satellite basedpositioning of a mobile arrangement with assistance data is proposed,wherein the mobile arrangement is adapted to communicate with thecommunication network and to acquire signals transmitted by satellitesof at least one satellite based positioning system. The network elementcomprises processing means. The processing means are adapted to convertavailable parameters of a dedicated orbit model describing a movement ofa satellite, which dedicated orbit model is defined for a particularsatellite based positioning system, into parameters of a common orbitmodel describing a movement of a satellite. The processing means arefurther adapted to provide the converted parameters as a part ofassistance data for the satellite based positioning.

According to the first aspect of the disclosure, moreover a mobilearrangement supporting a satellite based positioning of the mobilearrangement using assistance data is proposed. The mobile arrangementcomprises a satellite signal receiver adapted to acquire signalstransmitted by satellites of at least one satellite based positioningsystem. The mobile arrangement further comprises a communicationcomponent adapted to receive from the communication network assistancedata with parameters of a common orbit model describing a movement of asatellite. The mobile arrangement further comprises a processor orprocessing means adapted to estimate a position of a satellite of the atleast one satellite based positioning system based on receivedparameters of the common orbit model.

According to the first aspect of the disclosure, moreover a system isproposed which comprises the proposed network element of the firstaspect of the invention and the proposed mobile arrangement of the firstaspect of the invention.

According to the first aspect of the disclosure, moreover a firstsoftware code for supporting a satellite based positioning of a mobilearrangement with assistance data is proposed, wherein the mobilearrangement is adapted to communicate with a communication network andto acquire signals transmitted by satellites of at least one satellitebased positioning system. When being executed by a processing unit of anetwork element of the communication network, the software code realizesthe first method of the first aspect of the invention.

According to the first aspect of the disclosure, moreover a firstsoftware program product is proposed, in which the first software codeproposed for the first aspect of the invention is stored.

According to the first aspect of the disclosure, moreover a secondsoftware code for supporting a satellite based positioning of a mobilearrangement using assistance data is proposed, wherein the mobilearrangement is adapted to communicate with a communication network andto acquire signals transmitted by satellites of at least one satellitebased positioning system. When being executed by a processing unit of amobile arrangement, the software code realizes the second method of thefirst aspect of the invention.

According to the first aspect of the disclosure, moreover a secondsoftware program product is proposed, in which the second software codeproposed for the first aspect of the invention is stored.

The first aspect of the disclosure is based on the idea that the formatof parameters of an orbit model, which are provided as assistance datafor a satellite based positioning, could be decoupled from the format oforbit parameters that are defined in the scope of a respective satellitebased positioning system. It is proposed to this end that availableorbit parameters for a particular satellite based positioning system areconverted into parameters of a common orbit model. The common orbitmodel may, but does not have to be, defined in common for at least twosatellite based positioning systems. It is to be noted that the term“conversion” is meant to include as well a re-calculation of theparameters for the common orbit model.

It is an advantage of the first aspect of the disclosure that the sameorbit model can be used for the assistance data of various satellitebased positioning systems. With the common orbit model, a similarperformance in terms of accuracy can be achieved for all supportedsatellite based positioning systems. Also new satellite basedpositioning systems can be added easily. Thus, assisted positioning likeA-GNSS could be harmonized in various communication standards, forinstance in all cellular standards. In the mobile arrangements, thecommon orbit model facilitates moreover a hybridization, for example aGalileo-GPS hybridization which allows a mobile arrangement basingpositioning calculations on satellite signals of GPS satellites andGalileo satellites. It is also possible to use the common orbit model asa single orbit model for a particular satellite based positioningsystem, for instance instead of the GPS ephemeris and almanac model, andequally as a single orbit model for all positioning modes, for instancefor mobile station assisted GNSS and mobile station based GNSS. Using acommon orbit model thus reduces the number of data elements that have tobe supported in the communication standards. The size and complexity ofa positioning software in a mobile arrangement can be minimized whenusing the common orbit model in a mobile arrangement, possibly for ahybrid GPS/Galileo receiver, that dispenses with a standalonepositioning. That is, in case the mobile arrangement itself does nothave any software for decoding satellite navigation data, but onlysoftware supporting the proposed common orbit model, even though this isnot a preferred embodiment. The same common orbit model could even beused in addition for providing assistance data for terrestrialpositioning systems.

It is also an advantage of the first aspect of the disclosure thatpossible changes in the format of parameters of dedicated orbit models,like the parameters defined in the ICD-GPS-200, do not necessitatechanges in the converted parameters. The interface between thecommunication network and the mobile arrangements may thus stay thesame. Only the implemented parameter conversion has to be adapted.

It is also an advantage of the first aspect of the disclosure that theformat of the converted parameters is not tied to the format of theoriginal parameters. The conversion thus enables a provision of enhancedparameters and thus an improvement of the performance of an assistedpositioning.

The common orbit model may comprises for example more parameters than adedicated orbit model or parameters having a longer word length thancorresponding parameters of a dedicated orbit model. This allowsincreasing the accuracy of the orbit model and/or the validity time ofthe respective parameters. If the orbit model is more accurate, also theachievable positioning can be more accurate. If the parameters are validfor a longer time, fewer updates are required, which saves communicationbandwidth in the communication system.

The Jet Propulsion Laboratory of the California Institute of Technology(JPL) has already shown that it is possible to increase the accuracy andlife span of the satellite orbit models by increasing the word length ofthe orbital parameters. The International GPS Service, IGS, by JPLshares high-accuracy orbit models for a 48 hours period over theInternet. JPL publishes so called ultra-rapid orbit position data thatis valid and accurate at decimeter level at least +/−24 h, that is, 24hours ahead in time. The data is typically in sp3 format, which containssatellite position and velocity coordinates in ECEF (Earth CenteredEarth Fixed) frame, clock time and accuracy estimates sampled at someinterval, typically 15 min. The data is provided for the full GPSsatellite constellation. The data is not suitable for terminalpositioning as such but must be modeled e.g. by polynomial fitting toprovide a compact set of parameters for a terminal for satelliteposition and velocity extrapolation as function of time. For thepolynomial fitting, it is possible to use the “polynomial format”defined for the GPS ephemeris data. Modeling is also needed for thesatellite clock drifting. The IGS offers accurate information also forsatellite clocks that need to be modeled, for example, with polynomialstoo. A clock model is included in the standard satellite broadcast insubframe 1 in accordance with the GPS ICD, and it is provided as well incellular assistance. The clock model is typically assumed to be a partof ephemeris, but it is still a model of its own.

Global Locate Inc. has already shown that it is possible to increase theaccuracy and life span of the satellite orbit models by calculating theICD-GPS-200 compatible polynomial fit by using alternative fittingcriteria than used by GPS. The satellite ephemeris service by GlobalLocate Inc. uses the ICD-GPS-200 format to carry long-term orbit modelsfor the full GPS constellation. The life span of the long-term model canbe much longer than the life span of the broadcasted ephemeris. Thelatter approach, however, is still bound to the GPS ephemeris format.

The available parameters of a dedicated orbit model can be for examplebroadcast ephemeris or other orbital data, ephemeris or other orbitaldata provided by GNSS control segments, and/or ephemeris or otherorbital data provided by an external source, such as IGS.

The common orbit model can be based on Keplerian orbits and parametersused for the GPS ephemeris and almanac models. But it is also possibleto use various other representation to model the satellite positioninformation. Examples are Spline polynomials, Hermitean polynomials,piece-wise continuous polynomials, etc. By way of example, afourth-order polynomial model could be fitted into the true satelliteorbital trajectory given in an ECEF frame. The polynomial model can befitted using a criterion that minimizes the root mean of squared errors(RMSE). The polynomial model can then be used to extrapolate thesatellite position information forward in time.

Due to its sp3-format, including an ECEF position, an ECEF velocity andclock bias/drift accuracies (std), the IGS data is easy to use, forexample, in polynomial fitting. Modeling can be done e.g. by Spline orHermitean polynomial fitting so that the polynomials are fitted intosatellite position and velocity data for the period of the previous24-48 h. With the proposed common orbit model, there is more freedom toselect the parameters compared to simply using the “polynomial format”defined for the GPS ephemeris data. The polynomial order, the number ofparameters and the word lengths can be selected according to the desiredaccuracy and expected life span of the fit.

The common orbit model parameters which are eventually provided as apart of assistance data may comprise parameters for the entire satelliteconstellation of a particular satellite based positioning system, theentire satellite constellation of a plurality of satellite basedpositioning systems, or a part of one or more satellite constellations,depending on the capabilities of the mobile arrangement.

The supported satellite based positioning systems can be selectedarbitrarily. They may comprise for example GPS, GLONASS and Galileo, butequally EGNOS and WAAS, etc.

In addition to the converted parameters, the provided assistance datamay comprise in particular a reference time, for instance in form ofclock model parameters, and a reference location. It has to be notedthat also the common orbit model itself could contain, in addition to amodel for satellite position and velocity data, a model for satelliteclock bias and drift, a time reference for initialization, estimates forsatellite position, velocity and clock accuracy and possibly as well amodel for satellite attitude for phase wind-up correction for precisepoint positioning (PPP) calculation. The coordinate frame for positionand velocity models is advantageously the ECEF frame, as an earthrotation correction can be performed easily in an ECEF frame. Aconversion to local frames (East-North-Up) can be achieved with a simplematrix multiplication. IGS data may be comprised in the ECEF frame.

Further, the provided assistance data may comprise divers otherinformation. Examples are DGPS corrections, Real Time Kinematics (RTK)corrections and carrier phase measurements for satellite signals. For ahigh accuracy RTK positioning, reference is made to the document WO2004/000732 A1. Carrier phase measurements and RTK reference data, forinstance, are suited to support a high-accuracy positioning. It is to beunderstood that RTK corrections known for GPS may be adapted as requiredfor the support of a Galileo based positioning, etc. Further examples ofadditional assistance data are EGNOS and WAAS corrections. The databroadcast from geostationary EGNOS and WAAS satellites is difficult toreceive in high-latitude areas. The data may therefore be provided asnetwork assistance data instead, in particular if the common orbit modelis a short-term orbit model, as the current EGNOS/WAAS corrections assuch are not suitable for long-term orbit models. A further example ofadditional assistance data are short-term differential corrections forlong-term orbit models. A still further example of additional assistancedata are ionosphere model parameters and/or troposphere modelparameters. A still further example of additional assistance data areshort-term integrity warnings, which may be provided in the case of asudden satellite failure, in order to exclude the satellite fromposition calculation. A still further example of additional assistancedata are data bits of at least one satellite based positioning systemenabling a data wipe-off upon a request by a mobile arrangement. Datawipe-off is a method to improve the sensitivity in a satellite signalreceiver. For example, if GPS data content is unknown, it is possible tocoherently integrate the GPS signals only for 20 ms periods (1 GPS bit).In the case that the data bits are known, coherent signal integrationcan be continued over several GPS bits giving approximately 1.5 dB gainin sensitivity every time the integration time is doubled. For example40 ms (2 bits) could result in a gain of 1.5 dB, and 80 ms (4 bits) in again of 3 dB.

In one embodiment of the disclosure, the same or another network elementof the communication network further replaces a reference value in theconverted parameters that is based on a satellite based positioningsystem time by a reference value that is based on a communication systemtime. That is, the common orbit model is referenced to a communicationsystem time base only, and the satellite position information can thusbe calculated as a function of the communication system time instead of,for example, GPS or Galileo time.

The communication system time base can be used if the relation betweenthe GNSS system and communication system times is accurately known toenable accurate signal phase and Doppler prediction for a highsensitivity. For the communication system time, optional fields may beprovided in the assistance data, depending on the communication system.System specific information could be frame, slot and bit for GSM, systemframe number, slot and chip for WCDMA, and UTC time for CDMA.Considering slot and bit or chip, respectively, as well in GSM and WCDMAensures a sufficient resolution. The fields may also contain a timeuncertainty estimate (std) for estimating the uncertainty of signalphase and Doppler predictions.

In another embodiment of the disclosure, the common orbit model isreferenced to two time bases, for example UTC time and/or acommunication system time. The UTC time provides a universal timereference for all GNSS systems and makes it possible to evaluate thenumber of possible frame/superframe rollovers specific, for example, forcellular systems. The UTC time reference is also suited to remove theproblem of possible GNSS system time differences. GPS, Galileo andGlonass have different system times. Thus, biases between the systemtimes have to be known, if the systems are used in hybrid positioning assuch, for instance using one GPS signal to predict the phase of Galileosignals. This problem is removed by basing the model into a common timebase, that is, UTC time. The differences between the GNSS system timescan be compensated in the clock model. A common clock model can use forexample a second-order continuous polynomial fit having threeparameters, bias, drift and jerk. This is roughly the same as the clockmodel in the current GPS ICD. Still, any other model can be used aswell. The clock model could also include an accuracy or uncertaintyestimate for the clock error. The UTC time may also be a time stamp/IDfor the orbit model.

The assistance data can be transmitted to a particular mobilearrangement, in particular upon a request by the mobile arrangement.Alternatively, however, it could also be broadcast, for instance in arespective cell of a cellular communication system.

A mobile arrangement receiving the assistance data may then estimate aposition of a satellite of the at least one satellite based positioningsystem using the converted parameters.

II

According to a second aspect of the disclosure, a first method isproposed for supporting a satellite based positioning of a mobilearrangement with assistance data, wherein the mobile arrangement isadapted to communicate with a communication network and to acquiresignals transmitted by satellites of at least one satellite basedpositioning system. The method comprises replacing in the communicationnetwork a reference value that is based on a satellite based positioningsystem time in available parameters of an orbit model describing amovement of a satellite by a reference value that is based on acommunication system time. The method further comprises providing theparameters including the replaced reference value as a part ofassistance data for the satellite based positioning.

According to the second aspect of the disclosure, moreover a secondmethod is proposed for supporting a satellite based positioning of amobile arrangement using assistance data, wherein the mobile arrangementis adapted to communicate with a communication network and to acquiresignals transmitted by satellites of at least one satellite basedpositioning system. This method comprises receiving at the mobilearrangement assistance data from the communication network including atime stamp that is based on a communication system time. The methodfurther comprises determining at the mobile arrangement a communicationsystem time. The method further comprises estimating at the mobilearrangement a position of a satellite of the at least one satellitebased positioning system using the parameters in the assistance databased on the determined communication system time.

According to the second aspect of the disclosure, moreover a networkelement for a communication network supporting a satellite basedpositioning of a mobile arrangement with assistance data is proposed,wherein the mobile arrangement is adapted to communicate with thecommunication network and to acquire signals transmitted by satellitesof at least one satellite based positioning system. The network elementcomprising a processor or processing means. The processor or processingmeans are adapted to replace a reference value that is based on asatellite based positioning system time in available parameters of anorbit model describing a movement of a satellite by a reference valuethat is based on a communication system time. The processor orprocessing means are further adapted to provide parameters including areplaced reference value as a part of assistance data for the satellitebased positioning.

According to the second aspect of the disclosure, moreover a mobilearrangement supporting a satellite based positioning of the mobilearrangement using assistance data is proposed. The mobile arrangementcomprises a satellite signal receiver adapted to acquire signalstransmitted by satellites of at least one satellite based positioningsystem. The mobile arrangement further comprises a communicationcomponent adapted to receive from the communication network assistancedata with a time stamp that is based on a communication system time. Themobile arrangement further comprises a processor or processing meansadapted to determine a communication system time. The mobile arrangementfurther comprises a processor or processing means adapted to estimate aposition of a satellite of the at least one satellite based positioningsystem using parameters in received assistance data based on adetermined communication system time.

According to the second aspect of the disclosure, moreover a system isproposed which comprises the proposed network element of the secondaspect of the invention and the proposed mobile arrangement of thesecond aspect of the invention.

According to the second aspect of the disclosure, moreover a firstsoftware code for supporting a satellite based positioning of a mobilearrangement with assistance data is proposed, wherein the mobilearrangement is adapted to communicate with a communication network andto acquire signals transmitted by satellites of at least one satellitebased positioning system. When being executed by a processing unit of anetwork element of the communication network, the software code realizesthe first method of the second aspect of the invention.

According to the second aspect of the disclosure, moreover a firstsoftware program product is proposed, in which the first software codeproposed for the second aspect of the invention is stored.

According to the second aspect of the disclosure, moreover a secondsoftware code for supporting a satellite based positioning of a mobilearrangement using assistance data is proposed, wherein the mobilearrangement is adapted to communicate with a communication network andto acquire signals transmitted by satellites of at least one satellitebased positioning system. When being executed by a processing unit of amobile arrangement, the software code realizes the second method of thesecond aspect of the invention.

According to the second aspect of the disclosure, moreover a secondsoftware program product is proposed, in which the second software codeproposed for the second aspect of the invention is stored.

The second aspect of the disclosure is based on the idea that satellitepositions could be estimated based on parameters of an orbit model usinga communication system time instead of a satellite based positioningsystem time. To enable such an estimation, it is proposed that areference value in available parameters which is based on a satellitebased positioning system time is replaced by a communication system timebased reference value. For example, in the case of GPS ephemerisparameters, the TOE is replaced by a communication system time and incase of GPS almanac parameters, the TOA is replaced by a communicationsystem time. The relation between the satellite based positioning systemtime and communication system time must be known in the communicationnetwork in order to replace the reference values as proposed. But as theaccuracy for the time relation is not very tight, the relation can bemade available to the network in several ways.

It is an advantage of the second aspect of the disclosure that theassistance data is made independent of the satellite based positioningsystem time, and that the satellite based positioning system time doesnot have to be made available to the mobile arrangement.

The second aspect of the disclosure can be employed for any assistedsatellite based positioning system, for example for A-GPS or assistedGalileo.

If the communication network is a GSM network, for example, thecommunication system time may be defined by a respective combination ofa frame number, a time slot and a bit number. If the communicationnetwork is a WCDMA network, for example, the communication system timemay be defined by a respective system frame number, slot and chip. Allcurrent cellular terminals, for example, already decode the framenumbers. Thus, suitable time information is already available forsatellite position calculations, that is, for extrapolation of thesatellite positions using a cellular communication system time.

In the case of GPS, an extension of the current GSM and WCDMA cellularstandard with cellular time stamps is easy. There are already IEs andparameters for an accurate time transfer. The same parameters may beadded to the ephemeris and almanac IEs to be used instead of TOE andTOA, but having the same temporal information and use as TOW. Thisapproach would be backwards compatible too.

A mobile arrangement may receive the assistance data with the replacedreference value from the communication network. It may then determine acommunication system time and estimate a position of a satellite of theat least one satellite based positioning system using the parameters inthe assistance data based on a communication system time. With thesatellite position information, an accurate prediction of code phasesand Doppler frequencies of received satellite signals is enabled asknown in the art, even though a satellite based positioning system timewas not provided to the mobile arrangement.

A mobile arrangement having received assistance data from thecommunication network may provide by default a predetermined set offeedback items to the communication network. In existing approaches, theset of feedback items depends in contrast on the positioning mode, thatis, on whether the positioning is mobile station based or mobile stationassisted. The feedback data may include position information, like adetermined position of the mobile arrangement, a determined velocity ofthe mobile arrangement, a determined time of at least one satellitebased positioning system and determined measurement and/or positionuncertainties. The feedback data may further include measurements onreceived satellite signals and/or a relation between a satellite basedpositioning system time and a communication system time. The feedbackdata may also include Observed Time Difference (OTD) measurementsperformed on signals received from a plurality of base stations of acommunication network. The mobile arrangement may return OTDmeasurements to the communication network in the units of seconds, thatis micro or nanoseconds, instead of frame or subframe differences, inorder to make the information independent.

The mobile arrangement may also be required to maintain a relationbetween a time of the at least one satellite based positioning systemand a communication system time. If the mobile arrangement has obtaineda GNSS fix, it may associate to this end the current communicationsystem time, for example in terms of frame, subframe, slot, bit andchip, with the determined satellite based positioning system time.Alternatively, the mobile arrangement may receive an initial timerelation as assistance data. The time relation can be maintained forexample by evaluating time difference information from the network, byevaluating OTD measurements carried out in the mobile arrangement andestablishing a UTC-cellular time relation again if the uncertainty ofthe relation gets too large, or by evaluating GNSS time assistance fromthe network. For instance, in CDMA networks, GPS and UTC times areavailable by default. If a mobile arrangement has a valid time relation,this relation can be used to improve the performance in terms oftime-to-first-fix and sensitivity. Performance improvements can beachieved with a time relation having an accuracy of hundreds ofmicroseconds. The maintained time-relation may also be included in arequest for assistance data by the mobile arrangement to thecommunication network.

The communication network may collect the position data, the timerelation data and the OTD measurements provided as a feedback by mobilearrangements to create a database of time differences between the basestations. This data base can be used to deliver time-accurate assistancedata to mobile arrangements for improving the sensitivity withoutdelivering a satellite based positioning system time per se. If a mobilearrangement fails to calculate a position solution, the satellite signalmeasurements in the feedback, if any, can also be employed to estimatethe position of the mobile arrangement in the communication network.

III

According to a third aspect of the disclosure, a method is proposed forsupporting a satellite based positioning of a mobile arrangement usingassistance data, wherein the mobile arrangement is adapted tocommunicate with a communication network and to acquire signalstransmitted by satellites of at least one satellite based positioningsystem, and wherein the communication network is adapted to support atleast two different positioning modes. The method comprises transmittingat least one set of data that is independent of an employed positioningmode in at least one direction between the mobile arrangement and thecommunication network in the scope of a positioning of the mobilearrangement.

According to the third aspect of the disclosure, moreover a networkelement for a communication network supporting a satellite basedpositioning of a mobile arrangement with assistance data is proposed,wherein the mobile arrangement is adapted to communicate with thecommunication network and to acquire signals transmitted by satellitesof at least one satellite based positioning system. The network elementcomprises processing means, which are adapted to transmit at least oneset of data that is independent of an employed positioning mode to themobile arrangement and/or to receive at least one set of data that isindependent of an employed positioning mode from the mobile arrangementin the scope of a positioning of the mobile arrangement.

According to the third aspect of the disclosure, moreover a mobilearrangement supporting a satellite based positioning of the mobilearrangement using assistance data is proposed. The mobile arrangementcomprises a satellite signal receiver adapted to acquire signalstransmitted by satellites of at least one satellite based positioningsystem. The mobile arrangement further comprises a communicationcomponent adapted to transmit at least one set of data that isindependent of an employed positioning mode to a communication networkand/or to receive at least one set of data that is independent of anemployed positioning mode from the communication network in the scope ofa positioning of the mobile arrangement.

According to the third aspect of the disclosure, moreover a system isproposed which comprises the proposed network element of the thirdaspect of the invention and the proposed mobile arrangement of the thirdaspect of the invention.

According to the third aspect of the disclosure, moreover a firstsoftware code for supporting a satellite based positioning of a mobilearrangement with assistance data is proposed, wherein the mobilearrangement is adapted to communicate with a communication network andto acquire signals transmitted by satellites of at least one satellitebased positioning system. When being executed by a processing unit of anetwork element of the communication network, the software codetransmits at least one set of data that is independent of an employedpositioning mode to the mobile arrangement and/or receives at least oneset of data that is independent of an employed positioning mode from themobile arrangement in the scope of a positioning of the mobilearrangement.

According to the third aspect of the disclosure, moreover a firstsoftware program product is proposed, in which the first software codeproposed for the third aspect of the invention is stored.

According to the third aspect of the disclosure, moreover a secondsoftware code for supporting a satellite based positioning of a mobilearrangement using assistance data is proposed, wherein the mobilearrangement is adapted to communicate with a communication network andto acquire signals transmitted by satellites of at least one satellitebased positioning system. When being executed by a processing unit ofthe mobile arrangement, the software code transmits at least one set ofdata that is independent of an employed positioning mode to thecommunication network and/or receives at least one set of data that isindependent of an employed positioning mode from the communicationnetwork in the scope of a positioning of the mobile arrangement.

According to the third aspect of the disclosure, finally a secondsoftware program product is proposed, in which the second software codeproposed for the third aspect of the invention is stored.

The third aspect of the disclosure proceeds from the consideration thatcurrent assistance standards all provide different specifications fordifferent positioning modes. In order to unify and simplify thespecifications and the processing, it is proposed that at least one setof data that is exchanged between a mobile arrangement and acommunication network in the scope of a positioning is substantially thesame, no matter which positioning mode is employed.

The at least one set of data may belong for example to assistance datathat is transmitted from the communication network to the mobilearrangement. This allows providing as well that the operations performedin the mobile arrangement for the satellite based positioning aresubstantially the same irrespective of an employed positioning mode.

The at least one set of data may further belong to feedback informationtransmitted from the mobile arrangement to the communication network. Inthis case, the at least one set of data may comprise for instancemeasurement information for satellite signals acquired by the mobilearrangement. If the mobile arrangement determines itself its positionbased on the acquired satellite signals, the determined position may beadded to the common set of data.

It has to be noted that the position of the mobile arrangement can becalculated in both the mobile arrangement and the communication network.

IV

A further aspect of the disclosure proceeds from the consideration thatinstead of calculating any kind of correction data based on normalephemeris parameters, this correction data could be calculated based onparameters of a long-term orbit model that have a validity of at leastone day. As a result, the correction data can be utilized with thelong-term orbital parameters, not only with short term ephemerisparameters. The parameters may have been provided earlier than thecorrection data or be provided at the same time as the correction data.The correction data could be for instance WAAS, EGNOS or DGPS correctiondata, but also another or a new type of correction data.

Also the accuracy of parameters of a long-term orbit model degrades overtime. But with the proposed correction data, it is possible to extendeven the life span of these long-term orbital parameters.

The proposed correction data thus allows enhancing the accuracy and theintegrity of long-term orbit models. As the orbit model updates have tobe less frequent with accurate correction data, the amount of data thathas to be transferred between a communication network and a mobilearrangement is reduced and the load on the bandwidth is lowered. Alsothe correction models can be more accurate and long-term than existingmodels. Due to the nature of selective availability, DGPS corrections,for example, were initially developed to be very short-term correctionsand not very accurate. Because selective availability is nowadays turnedoff, a new type of DGPS correction can be designed to be very accurate.Further, a single format of correction data can be used for allsatellite constellations, like GPS, Galileo, Glonass, etc.

On the network side, a server may calculate the correction data for thelong-term orbit models in accordance with the third aspect of thedisclosure. The parameters of the long-term orbit model may be valid forseveral days and require some network bandwidth when being transmittedas a part of the assistance data to the mobile arrangement. Thecorrection data may be valid for several hours, but it requires lessbandwidth then a transmission of the parameters of the long-term orbitmodel. A respective set of correction data can be calculated in variousways. The actual correction data can be calculated for instance based onreal measurements from reference stations or based on an existingEGNOS/WAAS model. The form of the actual correction data does not dependon how the corrections were calculated.

On the side of a mobile arrangement, the correction data is received andused for correcting the parameters of a long-term orbit model before arespective estimation of a satellite position is performed. Theimplementation in the mobile arrangement may use the provided correctiondata in a similar manner as the conventional DGPS corrections. However,the calculation of a pseudorange correction amount per satellite dependson the correction model.

The model that is employed for computing the correction data can be forinstance some high-grade polynomial, like a 2^(nd) or 3^(rd) orderpolynomial, a piece-wise continuous polynomial, or even a more complexmodel.

It is to be understood that the proposed calculation of correction datacan be used with each of the first aspect of the invention, the secondaspect of the invention and the third aspect of the invention.

Any of the network elements of the first, the second and the thirdaspect of the disclosure can be for example a network server or a basestation of the communication network. The communication network in thefirst, the second and the third aspect of the invention can be forexample a cellular communication network like a GSM network, a WCDMAnetwork or a CDMA network, etc., but equally a non-cellular network,like a WLAN, a Bluetooth™ network or a WiMax network, etc. The mobilearrangements in the first, the second and the third aspect of theinvention may comprise a mobile communication device like a mobilephone, in which a satellite signal receiver is integrated.Alternatively, the satellite signal receiver can be an accessory devicefor the mobile communication device.

It is to be understood that all details described for the first aspectof the disclosure can also be combined with embodiments of the secondaspect of the disclosure, and vice versa.

BRIEF DESCRIPTION OF THE FIGURES

Other objects and features of the present invention will become apparentfrom the following detailed description considered in conjunction withthe accompanying drawings.

FIG. 1 is a schematic block diagram of a system supporting A-GNSS; and

FIG. 2 is a flow chart illustrating an operation in the system of FIG.1.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic block diagram of a system supporting A-GNSS inaccordance with an embodiment. The system avoids the necessity ofproviding GNSS time as assistance data and unitizes the provision ofassistance data.

The system comprises a base station 10 and a network server 20 of a GSMnetwork or of any other cellular communication network. The systemfurther comprises a first mobile station (MS1) 30, a second mobilestation (MS2) 40, GPS satellites (GPS SV) 50 and Galileo satellites (GPSSV) 60.

The base station 10 provides a radio interface to mobile stations 30, 40located in its vicinity. It comprises a processing unit 11 that is ableto execute various implemented software code components, including aparameter retrieval component 12, a reference time replacement component13, a message assembly component 14 and a feedback forwarding component15.

The network server 20 can be accessed by various base stations 10 of thecellular communication network. Moreover, it is connected to a GPScontrol server and to a Galileo control server (not shown). It comprisesa computer readable medium such as a memory 21 storing a database and aprocessing unit 22 that is able to execute various implemented softwarecode components likewise stored on a computer readable medium, includinga parameter computation component 23, a database updating component 24and a position estimation component 25.

The first mobile station 30 is a mobile arrangement which includes a GPSreceiver 31. The GPS receiver 31 comprises an acquisition and trackingcomponent 32, which may be realized in hardware and/or in software. Forinstance, for acquiring and tracking signals received from GPSsatellites 50, signal measurement tasks, including correlation tasks,could be performed by hardware under control of a software code which isexecuted by a processing unit of the GPS receiver 31.

The mobile station 30 further includes a cellular engine 35 as acellular communication component. A cellular engine is a module whichcomprises all components required for a conventional mobilecommunication between the mobile phone 30 and a cellular communicationnetwork and which may further be enhanced with additional functions. Thecellular engine 35 is or comprises to this end a data processing unitthat is able to execute various implemented software code componentsstored on a computer readable medium. In the presented embodiment, thesesoftware code components include an application component 36, a messageevaluation component 37 and a position estimation component 38. Theapplication realized by the application component 36 can be anyapplication which requires position related information, for example anavigation application or an application which ensures that specificservices are offered to a user of the mobile station 30 at specificlocations, etc. It is to be understood that, alternatively, theapplication component 36 and the position estimation component 38 couldbe executed by some other processing unit, for example by a processingunit of the GPS receiver 31.

The second mobile station 40 has a similar design as the first mobilestation 30, but instead of a GPS receiver it includes a Galileo receiveradapted to acquire and track signals received from Galileo satellites60. Alternatively, the second mobile station 40 could comprise forexample a hybrid GPS and Galileo receiver.

The determination of position information for a mobile station 30, 40 inthe system of FIG. 1 will now be described with reference to FIG. 2.FIG. 2 is a flow chart, which illustrates on the left hand side anoperation in one of the mobile stations 30, 40, in the middle anoperation in the base station 10 and on the right hand side an operationin the network server 20.

The network server 20 receives at regular intervals GPS ephemeris andalmanac parameters from the GPS control server for all available GPSsatellites 50, and corresponding Galileo parameters from the Galileocontrol server for all available Galileo satellites 60. The GPSparameters comply with the GPS interface control document (ICD) andbelong thus to a GPS specific ephemeris or almanac orbit model,respectively. The Galileo parameters comply with a Galileo ICD andbelong thus to a Galileo specific orbit model. The network server 20 mayalso receive additional information from the GPS control server, fromthe Galileo control server or from another entity. Such other entity mayprovide for instance EGNOS and WAAS corrections that are broadcast bygeostationary EGNOS and WAAS satellites.

The parameter computation component 23 converts the received GPSparameters into parameters of a common orbit model (step 201). Further,it converts the received Galileo parameters into parameters of the samecommon orbit model. The satellite for which the respective parametersare valid may be identified for example using indices containing notonly PRN, but also a constellation ID. The common orbit model is aspecification that describes orbital parameters and algorithms tocalculate satellite position information, like position, velocity andacceleration for GPS and Galileo satellites, and possibly as well forsatellites of any other GNSS, like GLONASS, EGNOS and/or WAAS. Inaddition, the common orbit model may allow calculating corrections tosatellite signals due to clock drifting. It has to be noted that anycorrection data, including WAAS-, EGNOS- and/or DGPS-like correctiondata, may be calculated or re-calculated specifically for the employedcommon orbit model.

By the parameter conversion, the parameters of different GNSSs areunitized, that is the number of parameters and the word length of theparameters is exactly the same for GPS and Galileo, etc. The parametersof the common orbit model may further be valid for a longer period oftime than the GPS ephemeris parameters. Moreover, they may define theposition of the satellites more accurately than, for instance, the GPSalmanac orbit model. This can be achieved for example by using moreparameters or by using longer word lengths than defined for theparameters transmitted by the satellites. Thus, the common orbit modelmay also be the only orbit model, for example, for GPS. It is to beunderstood that the conversion of the parameters comprises also are-calculation of the parameters.

The generated parameters of the common orbit model for a respectivesatellite comprise a reference value, which constitutes a reference timefor the included information that is based on the system time of theGNSS to which the satellite belongs, just like the TOE for GPS ephemerisdata or the TOA for GPS almanac data. For example, for a GPS satellite,the reference time is based on the TOW count of GPS, like the TOE or theTOA.

Now, the application component 36 of a mobile station 30, 40 may needsome position related information. For obtaining the requiredinformation, it may request assistance data for GPS and/or for Galileofrom the cellular communication network (step 301). The assistancerequest indicates the GNSS type that is supported by the mobile station30, 40.

When the base station 10 receives the assistance request, the parameterretrieval component 12 instructs the network server 20 to provide theparameters of the common orbit model for those satellites 50, 60 of thesupported GNSS or GNSSs that are currently visible at the location ofthe base station 10 (step 101). The instruction comprises anidentification of the base station 10 and an identification of the GNSSor GNSSs.

Thereupon, the parameter computation component 23 of the network server20 determines the satellites 50, 60 that are currently visible at thelocation of the base station 10 and that belong to the indicated GNSS orGNSSs (step 202). The current position of the satellites can bedetermined by means of the generated orbit model parameters. Thesatellites that are currently visible at an identified base station 10can thus be determined easily, if an association between the respectiveidentification of all base stations and their location is stored in thenetwork server 20, for example in the database in the memory 21. Theparameter computation component 23 selects the orbit model parametersfor the currently visible satellites and provides them to the basestation 10, possibly together with additional information. Suchadditional information may comprise for instance DGPS and RTKcorrections, EGNOS and/or WAAS corrections, short-term differentialcorrections, short-term integrity warnings and carrier phasemeasurements. Upon a special request by a mobile station 30, 40forwarded by the base station 10, the additional information may alsocomprise data bits for a data wipe-off.

The parameter retrieval component 12 of the base station 10 receives theprovided information and provides them to the reference time replacementcomponent 13.

The reference time replacement component 13 of the base station 10replaces the GNSS based reference time of the orbit model parameters foreach visible satellite 50, 60 by a cellular system based reference time(step 102). In case the cellular communication network is a GSM network,the cellular system based reference time can comprise for example aconstellation of a frame number, a time slot and a bit number{FN,TS,BN}, which represents the time of the GNSS based reference time.In case the cellular communication network is a WCDMA network, thecellular system based reference time can comprise for example a systemframe number (SFN), slot and chip, which represent the time of the GNSSbased reference time.

In order to be able to replace the GNSS based reference time with thecellular system based reference time, the base station 10 has to beaware of the current relation between the GNSS time and the cellularcommunication system time. There are several alternatives of providingthe base station 10 with this relation, since the requirement on theaccuracy of the relation is not very tight. It is sufficient to have arelation with an accuracy of 10-100 μs, or even with an accuracy of 1ms. A satellite moves at approximately 3.8 km/s, so the position errorin the satellite position in 1 ms is 4 meters at the most, which isnegligible.

In a first alternative, an LMU is associated to the base station 10. Inthis case, the LMU may determine the GNSS time and provides it to thebase station 10. The base station 10 may then determine the relationitself. It has to be noted, though, that it would be rather expensive toprovide all base stations of the network with an own LMU.

In a second alternative, there is only one LMU available in the cellularcommunication network, and the time differences to all base stations 10are measured by the cellular communication network at the site of thisLMU. For instance, a single base station in the network may be equippedwith an LMU to create a relation between a GNSS time and a cellularcommunication system time. The time differences between the LMU-equippedbase station and all other base stations 10 in the network are measuredin order to create a GNSS time to cellular communication system timerelation for any base station 10 in the cellular communication network.The time differences can be measured, for example, by collecting andevaluating OTD-measurements reported by default by mobile stations 30,40 to the cellular communication network.

In a third alternative, there is equally only one LMU available in thecellular communication network, and the time differences are measuredwith a Matrix solution. In this alternative, the mobile stations 30, 40are harnessed for measuring the base station time differences based onOTD-measurements. Cambridge Positioning Systems Ltd (CPS), for instance,has proposed a positioning and time keeping method using this approach.This method comprises more specifically measuring base station timedifferences at the mobile station, maintaining a corresponding databasein the mobile station and using this database for positioning and GPStime keeping. The method is called Enhanced-GPS (E-GPS). The use of theE-GPS method enables the cellular communication network as well toobtain the time differences in the cellular system between the LMU basestation and the other base stations 10, if the time differencesdetermined at the mobile stations 30, 40 are reported to the cellularcommunication network.

In a fourth alternative, no LMU is required in the cellularcommunication network. Instead, the mobile station 30, 40 provides therelation between the GNSS time and the cellular communication systemtime. If the mobile station 30, 40 already has a valid relation eitherfrom a previous positioning session or from the E-GPS solution, thisinformation can be sent to the cellular communication network along withthe assistance request. Some options for obtaining and maintaining avalid time relation in a mobile station 30, 40 will be described in somemore detail further below with reference to step 306. The base station10 may then use the time relation provided by the mobile station 30, 40to calculate the cellular system based reference time for the orbitmodel parameters.

Associating a GNSS time to a cellular communication system time has alsobeen described in U.S. Pat. Nos. 6,678,510 B2 and 6,748,202 B2, to whichit is referred.

Once the GNSS based reference time in the orbit model parameters foreach visible satellite 50, 60 of the supported GNSS has been replaced bya respective cellular system based reference time, the message assemblycomponent 14 assembles a message for each of these satellites 50, 60(step 103). The message is the same for any type of positioning mode.The message includes Information Elements (IE) with the orbit modelparameters, including the replaced reference time. In addition, it mayinclude a reference location, namely the known location of the basestation 10. Further, it may include any of the information provided bythe network server 20, information provided by some other entity, orinformation generated at the base station 10 itself.

The messages are then transmitted to the requesting mobile station 30,40.

It has to be noted that alternatively, the base station 10 couldassemble such messages at regular intervals for all respectively visiblesatellites 50, 60 and broadcast the messages to all mobile stations 30,40 located in the cell that is served by the base station 10.

The message evaluation component 37 of the mobile station 30, 40receives the messages and decodes the frame number, time slot and bitnumber in order to determine the cellular communication system time.Further, it extracts the information included in the received messages(step 302). An indication of the cellular communication system time,possibly in relation to the local time, and the extracted information,including the orbit model parameters, are provided to the positionestimation component 38.

The position estimation component 38 knows the algorithms of the commonorbit model. Based on these algorithms, the position estimationcomponent 38 extrapolates the respective satellite trajectory as afunction of the current cellular communication system time using theprovided orbit model parameters, and possibly taking account of theshort-term differential corrections, etc. (step 303). Based on theobtained satellite trajectory, the position estimation component 38 maylimit the possible propagation time of the satellite signal and theoccurring Doppler frequency in a conventional manner. With known limitsof the propagation time and the Doppler frequency, also the possiblecode phases that have to be checked can be limited. Such code phaselimitations are carried out for all satellites for which orbit modelparameters have been provided, except for those, for which a short-termintegrity warning has been provided in addition. A short-term integritywarning may be provided by the network server 20 via the base station 10whenever there is a sudden satellite failure.

The position estimation component 38 forwards the determined code phaselimitations and possibly further information included in the receivedmessages to the acquisition and tracking component 32. The acquisitionand tracking component 32 acquires the visible satellites (step 304).The information is used in a conventional manner to accelerate anacquisition of satellite signals by limiting the search options. Theacquisition and tracking component 32 may also be responsible fordecoding the navigation data in the acquired satellite signals. Theacquisition and tracking component 32 provides the measurement results,including any decoded navigation data, to the position estimationcomponent 38.

The position estimation component 38 may now determine the position ofthe mobile station 30, 40 in a conventional manner (step 305). That is,it determines pseudo ranges to those satellites 50, 60 of which signalshave been acquired. Further, it determines the exact satellite positionsbased on the decoded navigation data at the time of transmission of thesignals, which is indicated in the decoded navigation data and refinedby the measurement results. The position estimation component 38 thenuses the pseudo ranges together with the determined satellite positionsfor estimating the position of the mobile station. The positionestimation component 38 may equally determine in a conventional mannerany other desired position related information like velocity, GNSS time,measurement and position uncertainties, etc. The determined positionrelated information may then be provided to the application component 36for the intended use.

By default, the position estimation component 38 of the mobile station10 provides the determined position related information, the receivedmeasurement results and a relation between the cellular communicationsystem time and the GNSS time as feedback data to the cellularcommunication network. The feedback data is always the same irrespectiveof the employed positioning mode, except that the position of the mobilestation 10 may only be provided if it is determined by the mobilestation 10. The feedback data is forwarded by the feedback forwardingcomponent 15 of the base station 10 to the network server 20 (step 104).

The database updating component 24 of the network server 20 may collectthe position information, the relation between cellular communicationsystem time and GNSS time and in addition OTD measurements to create andupdate a database 21 of time differences between various base stations(step 203). This database 21 can be used to deliver time-accurateassistance data to mobile stations 30, 40 for improving the sensitivitywithout delivering GNSS time per se.

The positioning calculation component 25 of the network server 20 mayuse measurement results in the feedback data, if any, to estimate theposition of the mobile station 30, 40, in case the mobile station 30, 40failed to calculate a position itself (204).

The mobile station 30, 40 may also maintain the relation between thecellular communication system time and the GNSS time by default (step306). This can be done if the mobile station 30, 40 has obtained a validGNSS fix and has been able to associate the current cellularcommunication system time, for example in terms of frame, subframe,slot, bit and chip, with the GNSS time or has received the initialrelation as assistance data. In this case, the mobile station 30, 40 canreconstruct or recover the GNSS time at any moment just by estimatingthe elapsed time from the last GNSS fix using the cellular communicationsystem time and assuming that the mobile station 30, 40 does not movefrom one cell to another. If the mobile station 30, 40 moves from onecell to another, the relation between the GNSS time and the cellularcommunication system time has to be created again based on a new GNSSfix. Alternatively, the existing relation can be updated with the timedifference between the base station serving the previous cell and thebase station serving the current cell. The time difference can beobtained from OTD network assistance, assuming that there is a timedifference database available. The time difference can further beobtained from OTD measurements that the terminal performs itself. Thetime difference can further be obtained from the difference of timingadvance and/or round trip time measurements in the previous and thecurrent cell.

Further alternatively, the time relation can be maintained for examplefrom GPS time assistance from the cellular communication network. InCDMA networks, for example, GPS time is available by default.

If the mobile station 30, 40 has a valid GNSS-to-cellular communicationsystem time relation, this relation can be used to improve theperformance in terms of time-to-first-fix and sensitivity.GNSS-to-cellular communication system time relation having an accuracyof hundreds of microseconds is sufficient for these performanceimprovements.

The mobile station 30, 40 may return performed OTD measurements to thecellular communication network with each request for assistance data(step 301). It may return the OTD measurements for example in the unitsof seconds, in particular microseconds or nanoseconds, instead of frameor subframe differences, to make the information independent of thecellular communication system time.

It is to be noted that the described embodiment constitutes only one ofa variety of possible embodiments of the invention. For example, insteadof GPS and/or Galileo, other or additional GNSS could be supported aswell. As mentioned above, instead of a GSM network, any other type ofcellular communication network could be employed too. Also someprocessing could be shifted between different elements. By way ofexample, the reference time replacement could equally be performedcentrally for all base stations in the network server. Further, theprovided information can be varied. Moreover, instead of a new orbitmodel, the known GPS ephemeris and/or GPS almanac orbit models could beused for the GPS satellites and also for other GNSS satellites. Also oneor more orbit models standardized for another specific GNSS could beused. Further, the reference time replacement is not required, in caseGNSS time is readily available at the mobile stations, etc.

1. A method for supporting a satellite based positioning of a mobile device using assistance data, said method comprising at said mobile device: receiving assistance data from a communication network including parameters of an orbit model describing a movement of a respective satellite of a particular satellite based positioning system, wherein said parameters have a format that is different from a format of parameters of an orbit model defined for said satellite based positioning system or have been derived from another source than broadcast satellite data; receiving differential corrections for said received parameters of said orbit model; and correcting said received parameters of said orbit model based on said differential corrections.
 2. The method according to claim 1, wherein said orbit model of which parameters are received is more accurate than said orbit model defined for said satellite based positioning system.
 3. The method according to claim 1, further comprising at said mobile device estimating a position of said satellite based on said received parameters of said orbit model.
 4. The method according to claim 1, further comprising estimating a position of said mobile device in said mobile device using said received parameters of said orbit model.
 5. A method for supporting a satellite based positioning of a mobile device with assistance data, said method comprising: obtaining in a communication network parameters of an orbit model describing a movement of a respective satellite of a particular satellite based positioning system, wherein said obtained parameters have a format that is different from a format of parameters of an orbit model defined for said satellite based positioning system or are derived from another source than broadcast satellite data; and providing said obtained parameters and differential corrections for said obtained parameters as a part of assistance data for said satellite based positioning to at least one mobile device, wherein said differential corrections enable a mobile device to correct said parameters.
 6. The method according to claim 5, wherein said orbit model of which parameters are obtained is more accurate than said orbit model defined for said satellite based positioning system.
 7. The method according to claim 5, said method further comprising providing correction data for said orbit model of which parameters are obtained to said at least one mobile device.
 8. The method according to claim 5, further comprising estimating in said communication network a position of a mobile device to which said obtained parameters are provided using a feedback from said mobile device.
 9. The method according to claim 5, wherein said assistance data is transmitted to a particular mobile device upon a request by said mobile device.
 10. An apparatus supporting a satellite based positioning of said apparatus using assistance data, said apparatus comprising: a communication component adapted to receive assistance data from a communication network including parameters of an orbit model describing a movement of a respective satellite of a particular satellite based positioning system and differential corrections for said parameters of said orbit model, wherein said parameters have a format that is different from a format of parameters of an orbit model defined for said satellite based positioning system or have been derived from another source than broadcast satellite data; and a processing unit configured to correct said received parameters of said orbit model based on said differential corrections.
 11. The apparatus according to claim 10, wherein said communication component is further adapted to receive correction data for said received parameters of said orbit model, said apparatus comprising a processing component adapted to correct said received parameters of said orbit model based on said correction data.
 12. The apparatus according to claim 10, comprising a processing component adapted to estimate a position of said apparatus using received parameters of said orbit model.
 13. A apparatus for supporting a satellite based positioning of a mobile device with assistance data, said apparatus comprising a processing component adapted to obtain parameters of an orbit model describing a movement of a respective satellite of a particular satellite based positioning system, wherein said obtained parameters have a format that is different from a format of parameters of an orbit model defined for said satellite based positioning system or are derived from another source than broadcast satellite data; and adapted to provide said obtained parameters and differential corrections for said obtained parameters as a part of assistance data for said satellite based positioning to at least one mobile device, wherein said differential corrections enable a mobile device to correct said parameters.
 14. The apparatus according to claim 13, wherein said processing component is further adapted to provide correction data for said orbit model of which parameters are obtained to said at least one mobile device.
 15. The apparatus according to claim 13, wherein said processing component is further adapted to estimate a position of a mobile device to which said obtained parameters are provided using a feedback from said mobile device.
 16. A computer readable medium having software code stored thereon for supporting a satellite based positioning of a mobile device using assistance data, said software code realizing the method of claim 1 when being executed by a processing unit of said mobile device.
 17. A computer readable medium having software code stored thereon for supporting a satellite based positioning of a mobile device with assistance data, said software code realizing the method of claim 5 when being executed by a processing unit of a network element of a communication network.
 18. An apparatus comprising: means for receiving assistance data from a communication network including parameters of an orbit model describing a movement of a respective satellite of a particular satellite based positioning system and for receiving differential corrections for said received parameters of said orbit model, wherein said parameters have a format that is different from a format of parameters of an orbit model defined for said satellite based positioning system or have been derived from another source than broadcast satellite data; and means for correcting said received parameters of said orbit model based on said differential corrections.
 19. An apparatus comprising: means for obtaining in a communication network parameters of an orbit model describing a movement of a respective satellite of a particular satellite based positioning system, wherein said obtained parameters have a format that is different from a format of parameters of an orbit model defined for said satellite based positioning system or are derived from another source than broadcast satellite data; and means for providing said obtained parameters and differential corrections for said obtained parameters as a part of assistance data for said satellite based positioning to at least one mobile device, wherein said differential corrections enable a mobile device to correct said parameters. 